Method for preparing a glass convenient for trimming, a glass thus obtained, and method for trimming such a glass

ABSTRACT

A method for making appropriate for trimming a glass comprising a hydrophobic and/or oil-repellent surface coating is provided, as well as the glass itself, in which the surface of the glass is coated with a temporary protective layer imparting to the glass a surface energy at least equal to 15 mJ/m 2 .

BACKGROUND OF THE INVENTION

The present application claims priority to French Application No.01/06534 filed 17 May 2001, the entire text of which is specificallyincorporated by reference herein without disclaimer.

FIELD OF THE INVENTION

The present invention relates to the field of trimming glasses, moreparticularly ophthalmic glasses.

DESCRIPTION OF RELATED ART

An ophthalmic glass results from a series of molding and/orsurfacing/buffing operations determining the geometry of both convex andconcave optical surfaces of said glass, followed by appropriate surfacetreatments.

The last finishing step of an ophthalmic glass is a trimming stepconsisting in machining the glass edge or periphery so as to conform itto the required dimensions for adapting the glass to the glass frame inwhich it is intended to be accommodated.

Trimming is generally carried out on a grinding machine comprisingdiamond abrasive wheels that perform the machining step as definedhereabove.

The glass is held during such a step by axially-acting clampingelements.

The relative movement of the glass relative to the abrasive wheel iscontrolled, generally digitally, so as to get the required shape.

As it is obvious, it is absolutely imperative that the glass be firmlyheld during such a movement.

Therefore, before any trimming step, an glass-holding step is performed,i.e. a holding means or acorn element is positioned onto the convexsurface of the glass.

A holding pad, such as a self-adhesive sticker, for example a two-sidedadhesive, is arranged between the acorn element and the glass convexsurface.

The so-equipped glass is positioned onto one of the above-mentionedaxial clamping members, the second axial clamping element thus clampingthe glass onto its concave surface by means of an abutment, generallymade in an elastomer.

During the machining step, a tangential torque stress is generated onthe glass, which can result in the glass rotating relative to the acornelement if the glass-holding system is not efficient enough.

The efficient glass-holding mainly depends on the good adhesion at theinterface between the holding pad and the glass convex surface.

The latest generation ophthalmic glasses most often comprise hydrophobicand/or oil-repellent anti-stain surface coatings associated withanti-reflection coatings.

These are most often fluorosilane-type materials that reduce the surfaceenergy so as to prevent adhesive greasy stains which are thereby easierto remove.

One of the problems generated by this type of surface coating is thatthey achieve such an efficiency that the adhesion at the interfacepad/convex surface is thereby altered, even compromised for the mostefficient hydrophobic and/or oil-repellent coatings.

It becomes therefore more and more difficult to perform satisfactorytrimming steps, more particularly for polycarbonate glasses the trimmingof which results in much more important stresses than for othermaterials.

As a result of an inadequately performed trimming step, the glass ispurely and simply ruined.

SUMMARY OF THE INVENTION

One of the objects of the invention aims at offering a means allowing toperform the trimming step for a glass comprising at the surface ahydrophobic and/or oil-repellent coating, such means being able to beincorporated into the glass manufacturing process and being easy to beimplemented by the operator performing the trimming step.

Such a technical problem is solved according to the invention in that atemporary protective layer imparting to the glass a surface energy atleast equal to 15 mJ/m² is coated onto a glass comprising a hydrophobicand/or oil-repellent surface coating.

Consequently, a sufficient adhesion at the interface holding pad/glasscan be achieved for pads conventionally used in the technical field.

DETAILED DESCRIPTION OF THE INVENTION

It has already been previously suggested to coat temporary layers onophthalmic glasses, but essentially with a view to ensuring theirprotection against scratches and damages which might occur when beinghandled. This is the case, for example, in the Patent Application WO00/68326 relating to a method for manufacturing composite optical itemsfrom laminated optical films, the surface of such films having beenpreliminarily protected with a protective layer that can subsequently bedissolved.

In the present application, it is meant under the term “glass” anyorganic or mineral glass substrate, either treated or not, dependingwhether it comprises one or several various types of coatings or whetherit remains bare.

When the glass comprises one or more surface coatings, the expression“to coat glass” means that a layer is applied on the glass outercoating.

The surface energies are calculated according to the Owens-Wendt methoddescribed in the following reference: “Estimation of the surface forceenergy of polymers”, Owens D. K., Wendt R. G. (1969) J. APPL. POLYM.SCI, 13, 1741-1747.

The glasses treated using the method of the invention are glassescomprising a hydrophobic and/or oil-repellent surface coating andpreferably glasses comprising both a hydrophobic and/or oil-repellentsurface coating laid onto a mono- or a multilayered anti-reflectioncoating.

In fact, hydrophobic and/or oil-repellent coatings are generally appliedonto glasses having an anti-reflection coating, more particularly in amineral material, so as to reduce their strong tendency to staining, forexample, towards greasy deposits.

As previously mentioned, the hydrophobic and/or oil-repellent coatingsare obtained by the application, onto the anti-reflection coatingsurface, of compounds reducing the glass surface energy.

Such compounds are described in full detail in the prior art, forexample, in the following documents U.S. Pat. No. 4,410,563, EP-0 203730, EP-749 021, EP-844 265 and EP-933 377.

Silane-based compounds bearing fluorinated groups, more particularlyperfluorocarbonate or perfluoropolyether group(s) are most often used.

By way of examples, silazane, polysilazane or silicone compounds can bementioned which comprise one or more fluorinated groups such asmentioned hereabove.

A known method is to deposit on the anti-reflection coating compoundsbearing fluorinated groupings and Si—R groupings, R being a —OH group ora precursor thereof, preferably an alkoxy group. Such compounds are ableto conduct, at the anti-reflection coating surface, directly or afterhydrolysis, polymerization and/or crosslinking reactions.

The application of compounds reducing the glass surface energy isconventionally carried out by immersion of said compound into asolution, by centrifugation or by deposit in steam phase, among others.Generally, the hydrophobic and/or oil-repellent coating has a thicknesslower than 10 nm and more preferably lower than 5 nm.

The invention is preferably implemented on glasses comprising ahydrophobic and/or oil-repellent surface coating imparting a surfaceenergy lower than 14 mJoules/m² and more preferably lower than or equalto 12 mJ/m².

The temporary protective coating will increase the glass surface energyup to a value of at least 15 mJoules/m².

It may be applied on an area covering all of at least one of the twoglass faces or only on the area intended to receive the contact of theholding pad of said glass.

More precisely, it is usual to put the holding pad, associated with theacorn element, onto the glass convex face. It is therefore possible tocoat with the protective layer all the convex face or, alternatively,only a central area of the convex face, using a mask or any otherappropriate technique.

The deposit may uniformly coat the corresponding area, i.e., it shows acontinuous structure, but it can also show a discontinuous structure,such as a weave shape.

In such a case, an intermittent deposit is formed, the surface thereofbeing still sufficient so as to allow the required adhesion of theholding pad.

The coatings with discontinuous structure can be obtained bytampography.

As a result of coating the temporary protective layer, a glass isobtained which is appropriate for trimming.

This means that after trimming according to the invention, the glasswill have the required dimensions so as to be suitably inserted into theframe it is intended to be inserted into.

More precisely, such a result is achieved when the glass, during thetrimming operation, is subjected to a maximum off-centring of 2°.

An optimum ability to trimming corresponds to a glass having anoff-centring lower than or equal to 1°.

The protective layer is made of any material enabling to increase thesurface energy with hydrophobic and/or oil-repellent properties and ableto be eliminated during a subsequent later operation in the trimmingstep.

Evidently, the material should be such that it does not definitely alterthe surface properties of the hydrophobic and/or oil-repellent coatingand that after the latter has been eliminated, the optical and the glasssurface properties are globally identical to those the glass used toshow before the protective layer was laid.

Preferably, the temporary protective layer is a mineral layer, and moreparticularly, a fluoride or a mixture of metallic fluorides, an oxide ora mixture of metallic oxides.

Examples of fluorides can include magnesium fluoride MgF₂, lanthanumfluoride LaF₃, aluminium fluoride AlF₃ or cerium fluoride CeF₃.

Useful oxides are titania, alumina, zirconia or praseodymium oxide.

Alumina and praseodymium oxide mixtures are recommended.

A particularly recommended commercially available material is the PAS02from Leybold Corporation.

The protective layer may be laid with any conventional appropriatemethod.

Generally, the anti-reflection, hydrophobic and/or oil-repellentcoatings are laid by evaporation, in vacuum bells, and it is desirableto lay the temporary protective layer using the same technique, whichmakes it possible to carry out all the operations successively, with nounduly handling with the glasses between two steps.

When it is made of a mineral material, the protective layer thickness ispreferably lower than 50 nm, and generally ranges from 1 to 50 nm andmore preferably ranges from 5 to 50 nm.

Generally speaking, if the protective layer thickness is too low, thereis the risk that the surface energy will be insufficiently modified.

If, on the other hand, the protective layer thickness is too high, moreparticularly for essentially mineral layers, the inventors have foundout that mechanical stresses were likely to occur within the layer,which can be deleterious for the expected properties.

Preferably, and more particularly when the temporary protective layer islaid wholly on one of the glass faces, the material shows some degree oftransparency allowing to carry out on the glass conventional powermeasurements with a front-focimeter.

Thus, the glass appropriate for trimming according to the inventionpreferably shows a transmission of at least 18%, more preferably atleast 40% according to the ISO8980/3 standard.

As an alternative to the above-mentioned materials of mineral nature,conventional inks and/or the resins forming such ink binding agent canbe used for marking the progressive ophthalmic glasses.

In such a case, much higher thickness can be coated than is the case inpurely mineral layers.

The required thickness can then range from 5 to 150 microns.

Alkyd type resins are particularly recommended.

The glass appropriate for trimming according to the method of theinvention can be subjected to a wholly conventional trimming operation,except that, in a final step, the temporary protective layer should beremoved.

Thus, the invention also relates to a method for obtaining a trimmedglass having a hydrophobic and/or oil-repellent surface property,characterized in that it comprises the following steps of:

1) selecting a glass appropriate for trimming according to theinvention,

2) holding said glass by an acorn element,

3) trimming said glass,

4) removing the acorn element from said glass,

5) recovering the thus trimmed glass, and

6) removing the temporary protective layer so as to restore the glass inits hydrophobic and/or oil-repellent surface properties.

As indicated hereabove, the proper trimming step 3) is conventional andis known to the man of the art.

It will consequently not be described in full detail.

It can be however stated that the preferentially used holding pads aredouble-sided self-adhesive stickers, for example, adhesives from 3M.

The temporary protective layer removing step may be carried out eitherin a liquid medium or by dry wiping or by a successive application ofboth methods.

The liquid medium removing step is preferably carried out by with anacidic solution, more particularly with an orthophosphoric acidicsolution, at molarities ranging from 0.01 to 1 N.

The acidic solution may also comprise surfactants, either anionic,cationic or amphoteric.

The temperature at which the removing step is carried out is variable,but generally, the removing step is carried out at room temperature.

The temporary protective layer removal may also be enhanced by amechanical action, preferably through using ultrasounds.

Generally, after the treatment with the liquid medium such as with anacidic solution, by dry wiping or a combination of both, the removingstep comprises a cleaning step with an aqueous solution having a pHsubstantially equal to 7.

At the end of the temporary protective layer removal, the glass showsoptical and surface features of the same order, even quasi identical tothose of the initial glass, comprising the hydrophobic and/oroil-repellent coating.

The advantages associated to the invention are numerous.

The method according to the invention is easy to use.

More particularly, the man of the art may use conventional grindingmachines and trimming methods, without having to modify them, or in anextremely restricted way.

The temporary protective layer removing step is fast.

Glasses appropriate for trimming according to the invention, moreparticularly glasses comprising a temporary protective layer of mineralmaterial, may be subjected to markings using various inks, commonly usedby the man of the art, for progressive glasses.

The following examples illustrate the present invention.

Example 1 1.1. Preparation of Glasses Comprising a Hydrophobic andOil-Repellent Coating

Organic glasses are prepared, bearing three anti-abrasion,anti-reflection, hydrophobic/oil-repellent coatings that are coated insaid order on the substrate.

ORMA® organic glasses, having a −2.00 diopter power, obtained bypolymerizing glycol diethylene diallyl carbonate (CR 39® monomer), andcomprising an anti-abrasion coating of the polysiloxane typecorresponding to example 3 of Patent Application EP-614,957 in theApplicant's name, are heated in a drying-room for 3 hours at atemperature of 100° C.

The glasses are subsequently placed in a LEYBOLD 1104 vacuum treatmentdevice, provided with an electron gun and of a Joule effect evaporationsource.

A secondary vacuum is created by pumping the substrates, without heatingthem.

With the electron gun, 4 high index (HI)/low index (BI)/HI/BIanti-reflection optical layers are successively evaporated: ZrO₂, SiO₂,ZrO₂, SiO₂.

Thereafter, a hydrophobic and oil-repellent coating is applied byevaporation of an OPTOOL DSX brand product (a compound comprisingperfluoropropylene patterns) commercialized by DAIKIN corporation.

The product in a liquid form is poured into a copper capsule, the liquidis then allowed to dry at room temperature and at atmospheric pressure.

The copper capsule is then placed in a Joule effect crucible.

The product evaporation occurs under secondary vacuum.

The coated layer thickness is lower than 10 nm.

The coating thickness checking is performed using a quartz scale.

1.2. Coating of the Temporary Protective Layer

The temporary protective layer is then performed by evaporation coating.

A material identified as PASO 2, which is an alumina and praseodymeoxide mixture, commercialized by Leybold Corporation, is evaporatedusing an electron gun.

The evaporation is non reactive (without oxygen).

The physical thickness of the coated protective layer is 25 nm.

The coating thickness checking is performed using a quartz scale.

The glass is recovered after heating the enclosure and then put underthe treatment chamber atmosphere.

1.3. Trimming

The glass resulting from step 1.2 is subjected to a conventionaltrimming operation on a grinding machine from Essilor corporation.

As a holding pad a 3M self-adhesive sticker is used with a 25 mmdiameter and an acorn element from Essilor corporation having the samediameter.

The plastic:polycarbonate preform grinding machine has a 155 mm diameterand runs at 2850 tpm.

Upon the trimming operation, the glass off-centring is lower than 1°.

At that stage, the recovered trimmed glasses can be directly insertedinto the frame they are intended to be inserted into, followed by atreatment according to the following step 1.4 or treated according tostep 1.4 before being inserted into the frame.

1.4. Protective Layer Removal

For this step, an ultra-sound small vessel is used of the B2200 E2BRANSON model.

Ultra-sound power: 60 watts

Ultra-sound frequency: 47 kHz/−6 kHz

The glasses obtained in step 1.3 are immerged into a 0.1 N dilutedorthophosphoric acidic solution at room temperature (with ultra-soundsand without heating) for a period of time of 2 minutes, then rinsed withwater or isopropyl alcohol and wiped.

The resulting glasses show excellent optical features as well asexcellent hydrophobic and oil-repellent properties.

Example 2

Steps 1.1, 1.2 and 1.4 from example 1 are identically reproduced,excepted that they are performed on plane blades, of the same materialas the ORMA® CR39® substrates.

The contact angles are measured at the various steps of the method.

Using plane blades makes these measurements easier.

The contact angles have been measured:

In a air conditioned room: room temperature T°=21°±1° C., relativehumidity rate Rh=55%±5%.

With a GBX model Digidrop goniometer with 3 liquids: deionized water,glycerol and diiodomethane.

The surface energies are calculated according to the two-componentOwens-Wendt model with the DGD/fast 60 device from GBX Instrumentationsscientific corporation using a Windrop software.

The resulting results are listed in the following table:

TABLE 1 Plane substrate Plane substrate obtained Plane substrateobtained after after step obtained after step 1.2 1.4 (after removalstep 1.1 (with Paso 2 of Paso 2 (initial temporary temporary substrate)protective layer) protective layer) Water angle 118° ± 0.75 49° ± 3.5112° ± 0.95 Glycerol angle 105° ± 0.97 44° ± 0.9 103° ± 0.65Diiodomethane 92° ± 2   30° ± 3.8  91° ± 3.72 angle Polar 0.93 mJ/m²20.60 mJ/m² 2.29 mJ/m² component Dispersive 10.34 mJ/m² 31.99 mJ/m² 9.78mJ/m² component Total energy 11.4 mJ/m² ± 52.6 Mj/m² ± 11.7 mJ/m² ±(Owens - 0.5 0.8 0.5 Wendt)

It can be seen that with the Paso 2 based temporary protective layer,the surface energies are high: ophthalmic glasses made in such amaterial are thus able to be trimmed and allow a wide selection ofself-adhesive stickers to be used, as well as a wide selection of inksfor marking the glasses.

The surface energies achieved after the Paso 2 protective layer removalbecome again nearly identical to those achieved for the initial glass,comprising the anti-reflection coating and the hydrophobic andoil-repellent coating.

The surface characteristics of the hydrophobic and oil-repellent coatingare maintained.

Example 3

ORMA® glasses, having a −2.00 diopter power, are treated according tothe example 1, step 1.1 method, so as to obtain glasses withanti-reflection, hydrophobic and oil-repellent properties.

Said glasses are then treated by half: one half according to theprotocol described in example 1 step 1.2 is coated with a protectivelayer, while the other half, masked with a metallic mask, is not coatedwith a protective layer.

The glass part coated with the protective layer is then treatedaccording to the example 1, step 1.4 protocol, by immersion of half ofthe sample into an acid bath.

The following operations are performed on each of the two glass halves:

visual reflection Rv measurements and mean reflection Rm measurementsaccording to the ISO/WD 8980-4 standard,

colorimetric measurements of the tinting angle h and of the Chroma C*with a ZEISS spectrophotometer (angle 15°) and calculated in the CIE lab1964 system (L*, a*, b*).

The resulting results are listed in table II hereunder.

TABLE II Half with no protective Half with protective layer coating,layer coating followed by removal thereof h 135° ± 2° 135° ± 2° C* 7.27.3 Rv 0.72 0.71 Rm 0.74 0.75

The colorimetric values achieved after the Paso 2 layer has been coatedfollowed by the removal thereof are nearly identical to those of theglass part which has not received the Paso 2 coating: the Paso 2protective layer and its chemical removal do not modify the colorimetriccharacteristics of the anti-reflection coating.

Example 4

In this example, a temporary protective layer is coated by tampography.The coatings are done on glasses having a −2.00 diopter negative powermade in ORMA® and identical to those obtained from step 1.1 in example1.

An ink having a reference n°: 03XH622 2030 is used.

Diluent 4909

Manufacturer: Tiflex address: B.P. 3.01450.PONCIN.FRANCE.

10% diluent are added to the initial ink formulation so as to adapt thesolution viscosity.

The tampography device used is of the MTHV2 type.

(Manufacturer: Automation & Robotics)

The buffer being used is made of silicone.

Etched (depth 10 to 20 μm) and screened (20 to 40% filling rate) plate.

The ink is applied by tampography onto the glass.

Drying is done at room temperature or in a drying-room at 50° C. for aperiod of time higher than or equal to 5 minutes.

As a result, a discontinuous ink layer (screen) is obtained, theadhesion on the glass surface of which is sufficient so as not to bedamaged during transportation.

The trimming of the thus coated glass is then carried out placing a 3Mdouble-sided self-adhesive sticker onto the ink layer.

The resulting glasses are appropriate for trimming and can be insertedinto frames after trimming.

A comparative example is made on a glass which does not comprise anytemporary protective layer.

The glass is subjected to a high off-centring during the trimmingoperation and cannot be inserted into the corresponding frame.

The results obtained are listed in table III.

TABLE III Trimming Ink Plate depth screen Drying capacity Ex 1 Tiflex10-12 μm 20% air Yes Ex 2 Tiflex 10-12 μm 25% air Yes Ex 3 Tiflex 10-12μm 30% air Yes Ex 4 Tiflex 10-12 μm 40% air Yes Comparative — — — — NoExample

The invention claimed is:
 1. A glass, comprising a hydrophobic and/oroil-repellent coating onto which a temporary protective layer is coatedwhich imparts to the glass a surface energy at least equal to 15 mJ/m²,wherein the protective layer comprises one or more metallic fluorides.2. The glass of claim 1, wherein, before coating the protective layer,the glass comprising a hydrophobic and/or oil-repellent surface coatinghas an initial surface energy lower than or equal to 14 mJ/m².
 3. Theglass of claim 2, wherein the initial surface energy is lower than orequal to 12 mJ/m².
 4. The glass of claim 1, wherein the protective layeris coated on an area covering all of at least one of the two faces ofsaid glass.
 5. The glass of claim 1, wherein the protective layer iscoated only on an area adapted to receive the contact of a holding padof said glass.
 6. The glass of claim 1, wherein the protective layershows a continuous structure.
 7. The glass of claim 1, wherein theprotective layer shows a discontinuous structure.
 8. The glass of claim7, wherein the protective layer is screen-shaped.
 9. The glass of claim1, wherein the fluoride is MgF₂, LaF₃, AIF₃ or CeF₃.
 10. The glass ofclaim 1, wherein the protective layer has a thickness ranging from 1 to50 nm.
 11. The glass of claim 10, wherein the protective layer has athickness ranging from 5 to 50 nm.
 12. The glass of claim 1, wherein thehydrophobic and/or oil-repellent surface coating comprises a silanebearing fluorinated groups.
 13. The glass of claim 1, wherein thehydrophobic and/or oil-repellent surface coating has a thickness lowerthan 10 nm.
 14. The glass of claim 1, wherein the glass comprises ananti-reflection coating onto which the hydrophobic and/or oil-repellentcoating is coated.
 15. The glass of claim 14, wherein theanti-reflection coating is made of a mineral material.
 16. The glass ofclaim 14, wherein the anti-reflection coating comprises several layers.